1. Field of the Invention
The present invention relates to a printing system and printing method for designating and executing printing via the Internet, and a computer-readable medium.
2. Description of the Related Art
Conventionally, a terminal within an office intranet can use various services on the Internet. At this time, it is popular to install a firewall at the boundary between the intranet and the Internet. The firewall is introduced from a security standpoint: it is generally set to permit a connection from an intranet to the Internet but reject a connection from the Internet to the intranet. This can prevent illicit invasion from a terminal on the Internet side into the intranet. Under the circumstances, a communication system using a conventional Web service generally adopts PULL communication in which a client requests a server to acquire information and the server sends back the information as a response to the request.
Recently, a PUSH communication technique of transmitting information from a server serving as a source to a client is being developed. Examples of the PUSH communication technique are Comet and WebSocket.
In Comet, when a client transmits an HTTP (Hypertext Transfer Protocol) request to a server, the server holds it without quickly sending back the response. When information to be transmitted from the server to the client is generated later, the server transmits information to the client as a response to the held request. When a response has been received or a time-out occurs in the connection between the server and the client, the client transmits a request again. This implements an apparent persistent connection. At the timing when an event to which the server should respond occurs, the server can transmit a response without waiting for a request from the client.
WebSocket is a technique for bidirectional communication, which has been defined by Internet standardization groups W3C (World Wide Web Consortium) and IETF (Internet Engineering Task Force). Not HTTP but TCP (Transmission Control Protocol) connection is established and maintained, so mapping in the HTTP protocol becomes unnecessary, unlike Comet. In WebSocket, a connection start request originates from a client. Communication can be carried out a plurality of a number of times from both the client and server at free timings with one connection.
In the PUSH communication technique, a client within an intranet establishes and maintains a connection. Even in an environment where a firewall exists, the server can transmit information using the connection.
A printing system, which has conventionally been used only within an office intranet, is becoming usable via the Internet. The use of the Internet is implemented by PULL communication in which the presence of the firewall makes it hard for an intranet printer to acquire a print job in a print server on the Internet. Japanese Patent Laid-Open No. 2009-294920 discloses a printing system in which a mediation device within an intranet periodically sends an inquiry to a print server on the Internet, and when there is a print job to a printer within the intranet, receives it and transfers it to the printer.
However, in the conventional PULL printing system via the Internet, a print job can be received only at the timing to send an inquiry from a terminal within an intranet to a print server. For this reason, a waiting time may be generated until the printer actually receives a print job after the user issues a print instruction and the print job is accumulated in the print server. To shorten the waiting time, the interval of inquiry to the print server can be shortened. However, this causes another problem such as an increase in network traffic or an increase in processing load on the print server.
In another PULL printing system, simultaneously as the user issues a print instruction, the user's operation terminal transmits a print job acquisition instruction to a printer, and the printer acquires a print job from a print server. This form does not generate a waiting time till reception of the print job, but imposes a limitation in which the user's operation terminal and printer need to be able to communicate with each other. Thus, for example, the user cannot issue a print instruction from a mobile terminal outside the office to a printer in the office.
Recently, to solve the problems of the PULL printing system, there is proposed a printing system using PUSH communication. In the PUSH printing system, a printer within an intranet establishes a connection with a print server and always maintains the connection to allow the print server to transmit a print job to the printer at an arbitrary timing. Japanese Patent Laid-Open No. 2008-140275 discloses a technique in which a printer within an intranet performs communication at an appropriate timing before disconnection and maintains a connection established between the printer and a server.
In the above-mentioned PUSH printing system, each printer within an intranet establishes an persistent connection with a print server. In this case, as the number of printers increases, the processing load to manage persistent connections by the number of printers rises on the print server side. As a result, the operation of the print server becomes unstable or proper processing cannot be done.